Facile synthesis of pH-responsive gadolinium(III)-doped carbon nanodots with red fluorescence and magnetic resonance properties for dual-readout logic gate operations

The great challenge still exists in the synthesis of red-emissive carbon nanodots (C-dots) and the development of molecular logic devices with better operation stability for biological applications. In this study, gadolinium (III)-doped C-dots are synthesized by a new solvothermal approach using citric acid, urea and GdCl₃ as precursors. The as-prepared Gd³⁺-doped C-dots exhibit bright red fluorescence (FL) centered at 620 nm in an excitation wavelength-independent manner, and a high T₁ relaxivity (∼16.0 mM⁻¹ s⁻¹). More excitingly, the Gd³⁺-doped C-dots exhibit a pH-dependent response in not only FL behaviour but also magnetic resonance (MR) signal. When triggered by H⁺, OH⁻, or Cu²⁺, the Gd³⁺-doped C-dots can behave as a switch for FL emission and MR signal, leading to dual-readout and multi-addressable logic systems. Therefore, by employing the Gd³⁺-doped C-dots as logic gate with varying the chemical inputs, FL/MR dual-readout logic operations including IMP and NOR have been successfully demonstrated not only in all-aqueous media but also within the living HeLa cells. Together with the good biocompatibility and cell-permeability, the Gd³⁺-doped C-dots hold great potentials for real-time monitoring pH changes both in solution and biological cells, and even future evaluating cellular states via in-cell biocomputation.